Randomly select count entries evenly distributed from collection c and return them in a random order.

Description

Demo Code

/*/*from w w w .  j av  a 2  s  . c  om*/

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 */
import java.util.*;

public class Main{
    public static void main(String[] argv){
        List c = java.util.Arrays.asList("asdf","book2s.com");
        System.out.println(randomSelection(c));
    }
    private static LockssRandom random = new LockssRandom();
    /**
     * Randomly select <i>count</i> entries evenly distributed from
     * collection <i>c</i> and return them in a random order.  If
     * <i>count</i> is equal to <code>c.size()</code>, returns a random
     * permutation of <i>c</i>
     *
     * @param c The collection from which to select entries.
     * @param count The number of items to return.
     * @return A collection of items selected randomly from the list.
     * @throws IllegalArgumentException if count is non-positive or
     *         greater than the size of the collection.
     */
    public static List randomSelection(Collection c, int count) {
        int choiceSize = c.size();
        if (count < 0 || count > choiceSize) {
            throw new IllegalArgumentException("'count' negative "
                    + "or greater than collection size.");
        }
        if (count == 0) {
            return Collections.EMPTY_LIST;
        }
        Object[] arr = c.toArray();
        ArrayList result = new ArrayList(count);
        while (--count > 0) {
            int idx = random.nextInt(choiceSize);
            result.add(arr[idx]);
            arr[idx] = arr[choiceSize - 1]; // Replace chosen item with last item.
            choiceSize--;
        }
        result.add(arr[0]);
        return result;
    }
    /**
     * Randomly select one item from a list.
     *
     * @param c The list from which to select an item.
     * @return An item randomly selected from the list.
     */
    public static Object randomSelection(List c) {
        return c.get(random.nextInt(c.size()));
    }
    /**
     * Randomly select one item from a collection.  It is more efficient to
     * use {@link #randomSelection(List)} instead.
     *
     * @param c The collection from which to select an item.
     * @return An item randomly selected from the collection.
     */
    public static Object randomSelection(Collection c) {
        int idx = random.nextInt(c.size());
        Iterator iter = c.iterator();
        while (--idx >= 0) {
            iter.next();
        }
        return iter.next();
    }
}
Randomly select count entries evenly distributed from collection c and return them in a random order. - Android java.util

Description

Demo Code

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